For contact pieces in low-voltage power engineering switchgear, for instance in power switches as well as in direct-current, motor and auxiliary contactors, contact materials on the one hand of the silver-metal (AgMe) system and on the other hand of the silver-metal oxide (AgMeO) system are known. Representatives of the first system are, for instance, silver-nickel (AgNi) or silver-iron (AgFe); representatives of the second system are in particular silver-cadmium oxide (AgCdO) or silver-tin oxide (AgSnO2). In addition to this, there can be further metal oxides such as, in particular, bismuth oxide (Bi.sub.2 O.sub.3), copper oxide (CuO) and/or tantalum oxide (Ta.sub.2 O.sub.5).
The practical utility of a contact material having a base of silver-metal or silver-metal oxide is determined by the so-called electric contact properties spectrum. Controlling parameters are, in this connection, the lifetime number of switchings on the one hand, which is determined by the consumption of the switch piece, and the so-called excess temperature, i.e. the heating of the contact at the contact bridge which results essentially from the electrical resistance of the said contact structure. Sufficiently low tendency to welding-together of the contact pieces and resistance to corrosion are furthermore important since the switch properties can change with time due to long-time corrosion of the material in air-break switchgear.
From DE-A-1 608 211 there is already known an electric contact material of the silver-metal oxide system which can also contain iron oxide in addition to cadmium and/or tin oxide. Furthermore, in DE-C-38 16 895 the use of a silver-iron material with 3 to 30 wt. % iron and one or more of the additions manganese, copper, zinc, antimony, bismuth oxide, molybdenum oxide, tungsten oxide and chromium nitride in amounts of a total of 0.05 to 5% by weight, balance silver, are proposed for electric contacts. In addition, from DE-A-39 11 904 there is known a powder-metallurgy method for the production of a semifinished product for electric contacts from a composite material having a base of silver with iron, in which 5 to 50 wt. % iron is used as first secondary component and 0 to 5% by weight of a second secondary component consisting of one or more substances from the group containing the metals titanium, zirconium, niobium, tantalum, molybdenum, manganese, copper and zinc as well as their oxides and carbides. The iron in elementary form is obtained in this connection in particular by chemical precipitation. Finally, from JP-A-1/055345 a material of the aforementioned type is known which consists of a silver matrix in 0.5 to 20% by weight divided iron oxide particles, in which a part of the iron oxide is replaced by at least one of the oxides of nickel, cobalt, chromium, molybdenum, tungsten, cadmium, zinc, antimony, tin, bismuth, indium, lean, manganese, beryllium, calcium, magnesium or copper. The contact pieces produced therefrom are said to be excellent for use in switches due to good mechanical properties and high arc resistance.
The materials of the prior art in most cases do not satisfy at the same time all requirements of the spectrum of switch properties. In the final analysis, it is desired to achieve for the specific case of use an optimum of in each case the most important parameters which is adapted thereto.